The slow mode of the CERES scanning radiometers

Abstract

Clouds and the Earth's Radiant Energy System (CERES) instrument uses scanning radiometers on board the Terra and Aqua satellites use thermistor bolometers as detectors, with a sampling rate of 0.01s. During calibration testing a slow mode of detectors was found which had a magnitude of about three percent of the signal, and a characteristic time of 0.3 sec. To reduce the effect of this mode, a numerical filter was introduced. However, an analysis of the data from the CERES instruments aboard the Terra and Aqua satellites shows a difference of radiances in the forward scan compared to radiances from the backward scan. This difference is due to the slow mode not being characterized correctly. A focus of this work is to show results of setting slow mode filter parameters based on in-flight data. A gradient-based minimization strategy is employed to effectively find the filter parameters for each instrument to meet the performance goal of 0.15%. The newly designed numerical filters are to be used in processing the Edition 3 of CERES ERBE-like data products.

Putting all CERES instruments (Terra/Aqua) on the same radiometric scale

“…Radiation measurements go through carefully designed checks using on board calibration devices on each instrument: black bodies, a tungsten lamp and mirror attenuator mosaics (effectively solar diffuser plates). Other methods of checking the performance and stability include: (i) directly comparing instruments on the same platform, (ii) comparing CERES instruments on Terra and Aqua satellites, (iii) comparing CERES to other instruments, (iv) monitoring albedo of deep convective clouds (Priestley et al, 2007). However, recent analyses of the instruments' performance indicate their steady degradation estimated at about 1.5% over the duration of their mission (Priestley et al, 2006(Priestley et al, , 2007.…”

“…The spectral degradation is caused by the UV exposure, especially when an instrument is in the RAPS mode. The effort to bring out Edition 3 includes corrections to the data products to compensate for the observed changes in instruments' gains and spectral response, to eliminate the effect of a slow mode (Szewczyk et al, 2007); Aqua instruments still use ground offsets as a "cartwheel" maneuver to measure flight offsets was never implemented by the satellite. Spectral response functions for both Aqua instruments were examined and revised based on ground calibrations (Shankar, Thomas, Priestley, 2010) at the beginning-of-mission (BOM), and an initial gain change is also applied that is calculated based on ground-to-flight shifts in sensors response.…”

“…Other methods of checking the performance and stability include: (i) directly comparing instruments on the same platform, (ii) comparing CERES instruments on Terra and Aqua satellites, (iii) comparing CERES to other instruments, (iv) monitoring albedo of deep convective clouds (Priestley et al, 2007). However, recent analyses of the instruments' performance indicate their steady degradation estimated at about 1.5% over the duration of their mission (Priestley et al, 2006(Priestley et al, , 2007. The spectral degradation is caused by the UV exposure, especially when an instrument is in the RAPS mode.…”